Bonjour :)
1.
[tex]E = -a+b = -(-9)+3.5 = 9+3.5 = 12.5[/tex]
[tex]G = a+b = -9 + 3.5 = -5.5[/tex]
[tex]H = a-b = -9 - 3.5 = -12.5[/tex]
[tex]I = -a-b = -(-9)-3.5 = 9-3.5 = 5.5[/tex]
2.
[tex]A=7.2+(-5)-(-9.3)+2.2-5.8+(-3.6) = 7.2-5+9.3+2.2-5.8-3.6 = 4.3[/tex]